# 普通化學三題 太久沒算 請賜教

1. How many milliliters of a strongmonoprotic acid solution at pH = 4.12 must be added to 528 mL of the same acidsolution at pH 5.76 to change its pH to 5.34? Assume that the volumes are additive.The answer is ____21.0_____ mL. 2. (3%) Calculate the entropy change forthe following process: 10.0 g of oxygen (O2) gas at a pressure of1.0 bar and 25oC is combined in a 30.0-L container with 20.0 gof nitrogen (N2) gas initially at a pressure of 2.0 bar and 50oC. The resultingmixture is then heated at constant pressure to 100oC. The answer is ____13.2_____ (in Jmol-1K-1).

3. A constantcurrent is passed through an electrolytic cells containing molten MgCl2for 18 h. Write the half-cell reactions: 2Cl- → Cl2(g) + 2e- & Mg2+ + 2e- →Mg (l)If 4.8 × 105 g of Cl2 are obtained,what is the current in amperes? ___2.0 × 104 A__

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1. pH [H+] conc. Volume 5.76 1.738E-06 528 5.34 4.571E-06 528+V 4.12 7.586E-05 V 528* 1.738E-06+7.586E-05*V = 4.571E-06 *(528+V) V= 21 ml 2.

Youare asking for molar entropy change. Allcalculations will be in molar fraction. Moles Molar Fraction Oxygen 0.31 0.30 (xo2) Nitrogen 0.71 0.70 (xn2) Cp Cv Oxygen 29.1 20.81 Nitrogen 28.6 20.25 Entropychanges are due to Isobaric Processes (Delta S1), Isochoric Processes (Delta S2)and Gas mixing (Delta S3). Isobaric Processes: Delta S1 = Cp,o2 *ln (373 / 298)*xo2 + Cp,n2*ln (373 / 323)*xn2 = 1.96 + 2.88 = 4.84 Isochoric Processes: Delta S2 = Cv,o2 *ln (373 / 298)*xo2 + Cv,n2*ln (373 / 323)*xn2 = 1.40 + 2.04 = 3.44 Gasmixing: R= 8.314 DeltaS3 = -R*(xo2*ln(xo2)+xn2*ln(xn2) = 3.00 + 2.08 = 5.08 TotalEntropy Change = Delta (S1 + S2 + S3)

= 4.84+ 3.44+5.08 = 13.36 Jmol-1K-1 3.

4.8* 10^5 (g) = 4.8*10^5 /70.9*2 = 13540 moles of electrons 13540*96500= 1.3066 * 10^9 Coulombs Definitionof current 1Amp = 1 Coulomb/sec 1.3066* 10^9 /(18*3600) = 20163 Amps ~ 2.0 * 10^4 (Amps)

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